1. Field of the Invention
The present invention relates to a network system priority control method for implementing voice communication through an IP (internet protocol) network.
2. Description of the Related Art
In recent years, a voice network and a data network have been consolidated rapidly with the development of a network technology. Examples of the consolidated networks include a VoIP (Voice over IP) network for relaying a telephone network through an IP network.
In order to implement QoS (Quality of Service) required by a user, conventionally, a service has been provided in accordance with a priority required by the user. More specifically, priority control for transferring a packet in accordance with a priority has been carried out. For example, in the case in which a congestion is generated in the IP network, a loss of a packet and a delay are caused so that quality of a voice is deteriorated. For this reason, congestion control is carried out in the IP network. At this time, the congestion control is executed in accordance with a priority as one of the priority control operations. In other words, the order of packet transmission is changed in accordance with the priority or a packet having a low priority is discarded. Moreover, the transmission of a packet having a low priority to the IP network is suppressed. By such priority control, stable communication quality is provided to a user who requires a high priority (requires high voice quality).
FIG. 20 is a diagram showing an example of a conventional VoIP system. As shown in FIG. 20, in the VoIP system, an exchange 6 accommodating a plurality of extension terminals (an extension A and an extension B in FIG. 20) is connected to an IP network 5 through an IP network connecting device 1 and an IP network connecting device 2 accommodating a plurality of extension terminals (an extension C and an extension D in FIG. 20) is connected to the IP network 5, for example.
In order to control the priority control in the VoIP system, the IP network connecting devices 1 and 2 are to transmit a voice packet including header information indicative of a priority to the router 3 or 4 such that a router in the IP network 5 such as a router 3 or 4 can transmit a packet in accordance with a priority when the congestion is generated. Since the IP network connecting device 2 shown in FIG. 20 directly accommodates the extensions C and D, it can transmit a voice packet (see a packet P1 in FIG. 20) having a priority set to each of the extensions C and D can be transmitted to the router 4.
However, in the case in which the exchange 6 is connected to the IP network connecting device such as the IP network connecting device 1, the IP network connecting device 1 treats the exchange 6 as one extension terminal and does not recognize the extension terminals A and B accommodated in the exchange 6. For this reason, the IP network connecting device 1 transmits, to the router, a voice packet having a priority of the exchange 6 set, (see a packet P2 in FIG. 20). In the conventional art, accordingly, only one priority can be set to each extension terminal accommodated in an exchange. In other words, in the conventional art, a priority cannot be set to each extension terminal accommodated in the exchange. Consequently, only a low priority can be set to an extension terminal to which a high priority should have been set, so that proper communication quality cannot be provided.